Circuit for use with a loudspeaker for portable equipments

1. A circuit for use with a loudspeaker having a first differential input terminal and a second differential input terminal, the circuit comprising: a differential power amplifier having a first differential output terminal operatively connected to the first differential input terminal of the loudspeaker and a second differential output terminal operatively connected to the second differential input terminal of the loudspeaker; a first resistor disposed between the first differential output terminal of the differential power amplifier and the first differential input terminal of the loudspeaker; a second resistor disposed between the second differential output terminal of the differential power amplifier and the second differential input terminal of the loudspeaker, the circuit wherein it further comprises: a first resistive module arranged to generate on a respective output terminal a first control voltage, the first resistive module having a first input terminal connected to the first differential output terminal of the power amplifier and a second input terminal connected to the second differential input terminal of the loudspeaker, a second resistive module arranged to generate on a respective output terminal a second control voltage, the second resistive module having a first input terminal connected to the second differential output terminal of the power amplifier and a second input terminal connected to the first differential input terminal of the loudspeaker, the circuit being arranged to control the differential power amplifier on the basis of the first control voltage and the second control voltage.

2. The circuit of claim 1 , wherein the first resistive module comprises a third resistor and a fourth resistor, the third resistor having a respective first terminal corresponding to the first input terminal of the first resistive module and a respective second terminal, the fourth resistor having a respective first terminal corresponding to the second input terminal of the first resistive module and a respective second terminal, the second terminal of the third resistor and the second terminal of the fourth resistor being connected together in a node, the output terminal of the first resistive module being connected to said node.

3. The circuit of claim 1 , wherein the second resistive module comprises a fifth resistor and a sixth resistor, the fifth resistor having a respective first terminal corresponding to the first input terminal of the second resistive module and a respective second terminal, the sixth resistor having a respective first terminal corresponding to the second input terminal of the second resistive module and a respective second terminal, the second terminal of the fifth resistor and the second terminal of the sixth resistor being connected together in a node, the output terminal of the second resistive module being connected to said node.

4. The circuit of claim 3 , wherein the third resistor of the first resistive module, the fourth resistor of the first resistive module, the fifth resistor of the second resistive module and the sixth resistor of the second resistive module have substantially a same first reference value.

5. The circuit of claim 4 , wherein said second reference value is lower than the first reference value.

6. The circuit of claim 1 , wherein the first resistor and the second resistor have substantially a same second reference value.

7. The circuit of claim 1 , further comprising a differential stage having a first differential input terminal to receive the first control voltage and a second differential input terminal to receive the second control voltage, the differential stage having a first differential output terminal and a second differential output terminal.

8. The circuit of claim 7 , wherein the differential stage comprises: a first input NMOS transistor having the gate terminal corresponding to the first differential input terminal of the differential stage, the drain terminal operatively connected to a first reference voltage through a first current generator and the source terminal operatively connected to a second supply voltage through a first source resistor of the differential stage and a second current generator; a second input NMOS transistor having the gate terminal corresponding to the second differential input terminal of the differential stage, the drain terminal operatively connected to the first reference voltage through a third current generator and the source terminal operatively connected to the second reference voltage through a second source resistor of the differential stage and the second current generator.

9. The circuit of claim 8 , wherein: each of the NMOS transistors and each of the PMOS transistors representing the current generators of the differential stage, is electrically connected in series with a respective NMOS transistor and with a PMOS transistor, in a cascode configuration, each of the PMOS transistor of the first current mirror is electrically connected in series with a respective PMOS transistor in a cascode configuration and each of the PMOS transistor of the second current mirror is electrically connected in series with a respective PMOS transistor in a cascode configuration.

10. The circuit of claim 8 , wherein the differential stage further comprises: a first current mirror arranged to mirror the current passing on the first source resistor of the differential stage to a first output branch connected to the first differential output terminal of the differential stage; a second current mirror arranged to mirror the current passing on the second source resistor of the differential stage to a second output branch connected to the second differential output terminal of the differential stage.

11. The circuit of claim 10 , wherein: the first current mirror comprises a first PMOS transistor having the gate terminal connected to the drain terminal of the first input NMOS transistor of the differential stage, the source terminal connected to the first reference voltage and the drain terminal connected to the source terminal of the first input NMOS transistor of the differential stage, and the first output branch comprising a second PMOS transistor having the gate terminal connected to the drain terminal of the first input NMOS transistor of the differential stage, the source terminal connected to the first reference voltage and the drain terminal connected to the second reference voltage through a respective current generator, the first differential output terminal of the differential stage corresponding to the drain terminal of the second PMOS transistor of the first output branch.

12. The circuit of claim 10 , wherein: the second current mirror comprises a first PMOS transistor having the gate terminal connected to the drain terminal of the second input NMOS transistor of the differential stage, the source terminal connected to the first reference voltage and the drain terminal connected to the source terminal of the second input NMOS transistor of the differential stage, and the second output branch comprises a second PMOS transistor having the gate terminal connected to the drain terminal of the second input NMOS transistor of the differential stage, the source terminal connected to the first reference voltage and the drain terminal connected to the second reference voltage through a respective current generator, the second differential output terminal of the differential stage corresponding to the drain terminal of the second PMOS transistor of the second output branch.

13. The circuit according to claim 1 , further comprising a driving module having a first differential input terminal operatively connected with the first differential output terminal of the differential stage and a second differential input terminal operatively connected to the second differential output terminal of the differential stage, said driving circuit having a first differential output terminal operatively connected to a first differential input terminal of the differential power amplifier and a second differential output terminal operatively connected to a second differential input terminal of the differential power amplifier.

14. The circuit of claim 13 , wherein the driving module comprises: a digital processing unit; a digital-to-analog converter; and a analog-to-digital converter.

15. Portable equipment comprising a loudspeaker and a circuit according to claim 1 .